A model is presented that describes the heat transfer through a gypsum wallboard partition assembly incorporating the mass transport effects of water in liquid and vapor form. Sources of water include surface bound (adsorbed) water and hydrated water that is chemically bound with the crystal matrix of gypsum. Liberated water is allowed to migrate through the porous structure through molecular diffusion and pressure driven flow. Evaporation or condensation occurs when the partial pressure of water vapor with the pore space is less than or greater than the saturation pressure, respectively....